Temperature compensated valve for gas chromatography

ABSTRACT

Plungers and plunger assemblies for a diaphragm-sealed valve are provided. Each plunger is adapted to be received in a passage of the valve body and includes a base member and an upper member having a longitudinal play in this passage with respect to the base member. A resilient middle element is provided between the upper and base member. The base member is connected to a plunger actuating mechanism within the valve body. Optionally, the upper member may be self-aligning within the passage. The plunger can be used to compensate for temperature variations experienced by the valve in use.

FIELD OF THE INVENTION

The present invention generally relates to gas chromatography and moreparticularly concerns a valve therefor adapted to a wide range oftemperatures.

BACKGROUND

Chromatographic systems rely on the use of valves to allow reproduciblesample introduction and various column switching schemes.Diaphragm-sealed type valves are commonly used in such systems. Atypical diaphragm-sealed valve includes a valve cap having a pluralityof ports opening on an interface. Each port is linked to a passage inthe valve cap to which various analytical fitting and tubing may beconnected. A diaphragm valve also includes a valve body having aninterface opposite that of the valve cap. The diaphragm, generally madeof a polymer material, is compressibly positioned between the oppositeinterfaces of the valve body and valve cap. A main recess is usuallyprovided in the interface of the valve body, in which sits a matchingrecess in the diaphragm, allowing some clearance for fluid circulationbetween adjacent ports. This communication between ports can be stoppedthrough the use of plungers slideably mounted in the valve body. Eachplunger can press on the diaphragm between two adjacent ports, andtherefore prevent fluid communication therebetween.

Examples of diaphragm-sealed valve can for example be seen in U.S. Pat.Nos. 3,111,849; 3,140,615; 3,198,018; 3,376,894; 3,387,496; 3,417,605;3,439,542; 3,492,873; 3,545,491; 3,633,426; 4,112,766; 4,276,907;4,333,500; 5,601,115; 6,202,698 and 7,216,528.

One of the problems of prior art diaphragm valves for gas chromatographyis that the valve performance can vary greatly as a function of theoperating temperature to which it is submitted. Variations in leak ratecan be observed at moderate pressure, for example when the operatingtemperature is cycles such as is the case in temperature programmingmode, or simply when the valve is operate continuously at temperature upto 350° or 400° C.

This performance variation is related to the fact that materialdimensions of all the valve components, as well as the elasticity or thehardness of the polymer diaphragm, change with the temperature.

On the one hand, requirements for diaphragm-sealed valve design suitablefor gas chromatography applications involve tight manufacturingtolerances for flatness, parallelism, in the surface finishes, andlength of various components, especially the valve's plungers.Variations in plunger length will have a dramatic impact in the valveperformance. The total effect of temperature induced dimension changeswill generate leaks, particularly if the valve is subjected to rapid andlarge temperature variations that may generate distortions andcontinuous dimensions variation.

On the other hand, diaphragm variations in extreme conditions may becrucial as they can lead to permanent damage of the valve. In the priorart, the actuating pressure on the plungers, and the resulting forceapplied when a plunger is push against this diaphragm to interrupt fluidflow between two ports, does not vary with temperature. However, at highoperating temperatures, the polymer diaphragm become softer and thissame force may lead to permanent damage, by pushing away the materialunderneath the plunger area or simply by punching or leaving permanentmarking on the diaphragm.

Referring to FIGS. 1, 1A and 1B (PRIOR ART), there is shown a typicalpneumatic operating mechanism for the plungers of a diaphragm-sealedvalve. Such a mechanism includes two sets of plungers, respectivelydesignated as “normally closed and “normally opened” plungers, each setbeing attached to a corresponding piston. When a piston is moved into anupper position, it forces the corresponding plungers up against thediaphragm. Normally, the actuating pneumatic pressure of each piston isset to a value sufficient to generate the required force on thecorresponding plungers to seal the diaphragm between ports, without overstressing the diaphragm.

Diaphragm-sealed valves are normally operated with the help of a threeway electric solenoid valve. When the solenoid valve is powered ON (seeFIG. 2 (PRIOR ART)), the actuating pressure is applied into actuatingmechanism and when the solenoid valve is powered OFF (such as shown inFIG. 1B (PRIOR ART)), the pressure is evacuate from the actuator,normally to the atmosphere.

The stroke of the pistons is limited by the plungers pressing againstthe valve diaphragm. As a result, increasing the actuating pressureincreases the force applied on the diaphragm by the plungers. Typicalactuating pressure values for diaphragm-sealed valves range from 50 to65 PSIG. If the available actuating pressure from the solenoid valve ishigher, as is normally the case in a process plant environment where 125PSIG are usually available, a pressure regulator must be use to decreasethe supplied pressure to a safe level. This requires another piece ofhardware and associated tubing inside the instrument, increasing theoverall cost and necessitating a larger equipment inventory.

When a valve as shown in FIG. 1 is actuated at a typical actuatingpressure, for example 60 PSIG, and the temperature is ramped up, anotherproblem may appear, depend on the system configuration. The pressurizedvolume inside the valve is ramped up from ambient temperature to 300°C., generating a pressure rise of about 60 PSIG. This results in a finalpressure inside the system of roughly about 120 PSIG. This generates anuncontrolled extra force on the diaphragm that contributes to valveperformance diminution over the time. Since the resulting increase inforce acting on the diaphragm coincides with operating conditions wherethe diaphragm material is softened by the high temperature, operatingunder these conditions will reduce dramatically the valve performanceand lifetime.

There is therefore a need for a diaphragm-sealed type valve whichalleviates at least some of the drawbacks of the prior art.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, there is provided aplunger for a diaphragm-sealed valve, the valve having a valve bodyprovided with at least one passage extending in the valve body andopening on a diaphragm-contacting surface, a plunger-actuating mechanismbeing located within the valve body, said plunger being sized toslidably fit in a corresponding one of the at least one passage of thevalve body and comprising:

-   -   a base member operatively connectable to the actuating        mechanism;    -   an upper member projecting towards said diaphragm-contacting        surface when in said passage, said upper member having a        longitudinal play within said passage with respect to the base        member; and    -   a resilient middle element provided between the base member and        the upper member.

Advantageously, embodiments of the invention provide for thecompensation of temperature variation, and allow a wide range ofactuating pressure while keeping the valve performance at the same leveland allowing less stringent manufacturing tolerances, thereby reducingproduction costs.

Preferably, a transversal play is further provided between the uppermember and base member, In such embodiments, misalignments of theplunger relative to its corresponding passage may be compensated for byallowing the upper member of the plunger to align itself with thepassage, thereby improving the overall valve performances.

In accordance with another aspect of the invention, there is furtherprovided a plunger assembly for a diaphragm-sealed valve, the valvehaving a valve body provided with a plurality of passages extending inthe valve body and opening on a diaphragm-contacting surface, saidplunger assembly comprising:

-   -   a plunger-actuating mechanism located within the valve body; and    -   a plurality of plungers each slidably provided in a        corresponding one of the passage of the valve body, each plunger        comprising:        -   a base member operatively connected to the actuating            mechanism;        -   an upper member projecting towards said diaphragm-contacting            surface when in said passage, said upper member having a            longitudinal play within said passage with respect to the            base member; and        -   a resilient middle element provided between the base member            and the upper member.

In one embodiment, an adjustable attachment connects the base member ofeach plunger to the plunger-actuating mechanism, therefore allowing afine-tuning of the distance therebetween.

Other features and advantages of the present invention will be betterunderstood upon reading of preferred embodiments thereof with referenceto the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (PRIOR ART) is a top view of a valve according to prior art. FIG.1A is a cross-sectional view along lines A-A of FIG. 1; FIG. 1B is anenlargement of portion B of FIG. 1A, and is shown with the actuatingmechanism turned “OFF”.

FIG. 2 (PRIOR ART) shows an enlargement of a cross-sectional view of thevalve of FIG. 1, shown with the actuating mechanism turned “ON”.

FIG. 3 is a top view of a diaphragm-sealed valve provided with plungersaccording to embodiments of the invention.

FIG. 4A is a cross sectional view along lines A-A the valve of FIG. 3,and FIG. 4B is an enlargement of a portion of FIG. 4A, showing a portionof a plunger assembly according to an embodiment of the presentinvention before actuation.

FIG. 5A is a cross sectional view along lines A-A the valve of FIG. 3,and FIG. 5B is an enlargement of a portion of FIG. 5A, showing a portionof a plunger assembly according to an embodiment of the presentinvention after actuation.

FIG. 6 is a top view of a valve provided with a pressure reliefmechanism according to an embodiment of the invention.

FIG. 7A is a cross sectional view of the valve of FIG. 6 with thepressure relief mechanism actuated; FIG. 7B is an enlargement of aportion of FIG. 7A.

FIG. 8A is a cross sectional view of the valve of FIG. 6 with thepressure relief mechanism unactuated; FIG. 8B is an enlargement of aportion of FIG. 8A.

FIG. 9 a is a side view of a plunger according to an embodiment of theinvention; FIG. 9B is a cross-sectional view along lines B-B of FIG. 9A;FIG. 9C is a side view of the plunger of FIG. 9A from a perpendiculardirection.

FIGS. 10A and 10B are cross-sectional views of plungers according tovariants of the embodiment of FIGS. 9A to 9C, provided with differenttypes of resilient middle elements.

FIGS. 11A to 11C are cross-section views of plungers according to adifferent embodiment of the invention, shown with different types ofresilient elements.

FIG. 12 is a cross-sectional view of a plunger according to anotherembodiment of the invention, wherein a portion of the resilient middleelement is received within a recess in the base member.

FIG. 13 is a cross-sectional view of a plunger according to anotherembodiment of the invention, wherein the head member of the plunger isself-aligning.

FIG. 14 is a top view of a plunger according to another embodiment ofthe invention incorporating a self-aligning head member; FIG. 14A is across-sectional view taken along lines A-A of FIG. 14; FIG. 14B is across-sectional view taken along lines B-B of FIG. 14.

FIGS. 15A and 15B are perspective exploded views of plungers having anadjustable base section according to embodiments of the invention.

FIG. 16 is a cross sectional view of a portion of a plunger assemblyincorporating plungers according to the embodiments of FIGS. 15A and15B.

FIG. 17 is a cross-sectional view of a plunger according to yet anotherembodiment of the invention, where the upper member is not interlockedwith the base member.

FIG. 18 is a cross sectional view of a portion of a plunger assemblyincorporating plungers according to the embodiment of FIG. 17.

FIG. 19 is a graphic of the actuating pressure required to maintainproper sealing of a typical polymer diaphragm-sealed valve.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention generally relates to plungers and plungerassemblies for diaphragm-sealed valves, for example of type suitable forgas chromatography.

With reference to FIGS. 3, 4A, 4B, 5A and 5B there is show an example ofa portion of an improved plunger assembly for a diaphragm-sealed valve20, according to an embodiment of the invention. The valve 20 generallyincludes a valve body 22, a valve cap 24 and a diaphragm compressiblydisposed therebetween. For more detail on the construction of a valve ofthis type, reference can for example be made to international patentapplication published under no. WO/2009/073966. One or more passage 28extends in the valve body 22 and open on a diaphragm-contacting surface30. A plunger-actuating mechanism 32 is located within the valve body.

The illustrated embodiment shows a six (6) plungers valve, two (2) ofwhich being shown in FIGS. 4B and 5B. Of course, the present inventionmay be applied to diaphragm-sealed valves having a different number ofplungers. The term “plunger” is understood to mean a mechanicalcomponent driven by or against a mechanical force or fluid pressure. Theparticular construction of plungers 34 according to embodiments of thepresent invention will be explained further below.

Each plunger 34 is slideable in a corresponding passage 28 of the valvebody 22. Preferably, the diameter of a passage 28 is slightly largerthan that of its corresponding plunger 34. A guide sleeve (not shown)may surround the passage 28, for facilitating the movement of theplunger 34 into the passage 28. Preferably, when in the closed position,the contact area of each plunger 34 is pushed evenly throughout itssurface. Thus, all mechanic or fluid forces are transferred equally ontothe diaphragm 26. This design ensures that the plungers 34 remainsubstantially vertical when actuated.

According to embodiments of the invention, the plungers 34 arepreferably of two types, designated as “normally closed” (NC) and“normally open” (NO). In typical chromatography applications, theplungers 34 of a given type are actuated together, so that they areeither all in the closed position or all in the open position. As theirnames indicate, the normally closed plungers 34NC are biased towards theclosed position, whereas the normally opened plungers 34NO are biasedtowards the open position.

In the illustrated embodiment, it can be seen that the normally closedplungers 34NC have a length different than the length of the normallyopen plungers 34NO. The plunger-actuating mechanism 32 preferablyincludes a push plate 36 which extends within the valve body 22 inparallel to its diaphragm-contacting surface 30, and is movabletransversally thereto. The normally closed plungers 34NC are mounted onthe push plate 36. The plunger-actuating mechanism 32 further includesan upper piston 38 extending contiguously under the push plate 36. Thenormally open plungers 34NO are mounted on the upper piston 38. Aplurality of cavities 40 extend across the push plate 36 for allowingthe normally open plungers therethrough.

The plunger-actuating mechanism 32 further includes a lower piston 42extending contiguously under the upper piston 38 and rigidly connectedto the push plate 36. The lower piston 42 and push plate 36 thereforemove together within the valve body 22. Dowel pins (not shown) may beprovided to prevent the upper and lower pistons 38 and 42 from rotatingwith respect to each other and with respect to the valve body 22, andO-rings 44 are preferably provided to properly seal the upper and lowerpistons 38 and 42.

In the illustrated embodiment, a Belleville assembly 46, including aBelleville washer stack and a plate, cooperates with the lower piston42. The force on the Belleville assembly 46 is preferably controlled bya compression set screw 48. A bottom cap (not shown) may close the valvebody 22 at its bottom end. Of course, the Belleville assembly 46 may bereplaced by any other biasing means, such as standard springs or polymerbushings.

The upper piston 38 is biased downward by appropriate means. In theillustrated embodiment, disc spring 50 extend from within the valve body22 over the upper piston 38, and applies a downward force thereon whenno opposite force is in play. The normally open plungers 34NO mounted onthe upper piston 38 are therefore biased towards the open position. Inthe upward direction, the stroke of the upper piston 38 is limited by ashoulder 52 machined in the valve body 22.

The actuating mechanism 32 is operable for actuating the plungers 34 ofboth types between their open and closed positions thereof. This can beaccomplished in the current embodiment by controlling the distancebetween the upper and lower pistons 38 and 42. When not actuated, asshown in FIG. 4B, the two pistons 38 and 42 are in contact, as they arepushed towards each other by the Belleville assembly 46 and disc spring50. The actuating mechanism 32 preferably includes a pneumatic actuatorformed by the two pistons 38 and 42, the push plate 36 and theBelleville assembly 46, and further includes a solenoid valve or otherappropriate system for supplying pressurised gas between the upper andlower pistons 38 and 42 through a cylinder port. When the valve isactuated (see FIG. 5B), the gas will counterbalance the bias of bothpistons 38 and 42 by pushing the upper piston 38 upward, thus slidingthe normally open plungers 34NO towards the closed position, and thenpushing the lower piston 42 downwards, thus pulling the push plate 36downward and retracting the normally closed plungers 34NC towards theopen position. Removing the pressurized gas will have the oppositeresult, due to the biasing effect of the Belleville assembly 46 and discspring 50.

With reference to FIGS. 6, 7A, 7B, 8A and 8B, there is shown an optionalpressure relief mechanism which may be use in a valve as describedabove.

Oftentimes, after diaphragm valves are built and fully tested, they aresealed in plastic packages, packed and stored in inventory beforeshipping to customers. Depending on various factors such as marketdemand, inventory management, customer need and the like, valves arelikely to stay unused for weeks or months after their manufacture. Inaddition, in some circumstances a valve owner may temporarily shut downor remove a valve from active use for an undetermined amount of timebefore putting it in service again. While a valve is idle, its normallyclosed plungers are in their closed position and therefore apply aconstant pressure on the diaphragm. Depending on diaphragm material,this could lead to a permanent deformation of the diaphragm, and reducedefficiency of the valve. The pressure relief mechanism may therefore beused to lock the normally closed plungers in their open position whenthe valve is not in use.

In the illustrated embodiment, the valve body 22 preferably includes atleast one valve transverse passage 54 extending therethrough from a sideof the valve 22 to the lower piston 42. The lower piston 42 alsoincludes a piston transverse passage 56, which is aligned with the valvetransverse passage 54 of the valve body 22 when the lower piston 42 islowered, and the normally closed plungers 34NC therefore in the openposition. A locking pin 58 is also provided and insertable through thealigned transverse passages 54 and 56 of the valve body 22 and lowerpiston 42. In the illustrated embodiment two sets of transverse passagesand corresponding locking pins are shown, but it will be understood thatany number of passages and pins may be provided. In order to lock thevalve 20, the actuating mechanism is operated to lower the normallyclosed piston 34NC, preferably by supplying pressurized gas between theupper and lower pistons 38 and 42 as explained above. This brings thetransverse passages 54 and 56 of the valve body 22 and lower piston 42in alignment, and the locking pin 58 can be inserted therein. Once thelocking pin 48 is in place, the actuating mechanism can be deactivated,and both the normally closed and normally opened plungers 34NC and 34NOwill remain in their open position, leaving the diaphragm 26 free ofmechanical stress thereon. The locking pin 58 can be simply removed andthe valve 20 reactivated whenever the valve needs to be used again.

Referring to FIGS. 9A to 9C, there is shown a first embodiment of aplunger 34 according to an embodiment of the present invention. Eachplunger is made of three (3) separate sections: a base member 60, anupper member 62, and a resilient middle element 64. The base member 60is operatively connected to the plunger-actuating mechanism forcollaboration therewith. Preferably, the plungers 34 are affixed toeither the push plate or the upper piston through fixed fasteners suchas screws, which advantageously allows the valve to be fully operationalregardless of its orientation. It will therefore be understood by oneskilled in the art that the reference to the directions “up” and “down”or “upper” and “lower” throughout the present application is used forease of reference to the drawings, and is not meant to indicate apreferred orientation of the valve in use.

The upper member 62 projects towards the diaphragm-contacting surface ofthe valve body, and will therefore compress the diaphragm when theplunger is in the closed position. In some embodiments, the upper member62 is interlocked with the base member 60. By “interlocked”, it isunderstood that the upper member 62 and base member 60 are connecteddirectly or indirectly in such a fashion that they are part of a samemechanism. The upper member 62 has a longitudinal play within thepassage of the valve body with respect to the base member 60, that is,it is free to move vertically up and down over an appropriate distancewith respect to the base member 60.

The resilient middle element 64 is disposed between the base member 60and upper member 62. When the plunger is at rest, the resilient middleelement 64 preferably biases the upper member 62 away from the basemember 60. When the pistons are force downwardly, the base member pullsdown the upper member to clear the diaphragm.

Referring to FIGS. 9B, 10A and 10B, the upper member 62 of the plungerpreferably includes a head portion 66 which projects towards thediaphragm-contacting surface, a neck portion 68 which holds theresilient middle element 64 and an anchor portion 70 interlocked withthe base member 60. The resilient middle element 64 is preferably ringshaped, surrounds the neck portion 68 and its opposite ends 72 a and 72b respectively abuts on the under face of the head portion 66 and asurface of the base member defining an abutment surface 74. In theembodiments of FIGS. 9B, 10A and 10B, the abutment surface of the basemember extends on the top thereof.

Preferably, the anchor portion 70 of the upper member 62 has a widthgreater than its neck portion 68, and may for example be shaped as adisk as shown in the drawings in reference. The anchor portion 70 ispreferably received in a cavity 76 provided in the base member 60, thiscavity 76 being sized to provide a longitudinal clearance 78 for theanchor portion 70. In this manner, the upper member can move over acertain range along the longitudinal axis of the plunger 34, therebydefining a longitudinal play between the upper and base member 62 and60.

Preferably, the upper member 62 and base member 60 are machined todefine mating shapes as shown in the drawings. The base member 60further preferably includes a bore 82 extending longitudinally thereinand having opposite extremities 84 a and 84 b opening on the abutmentsurface 74 of the base member 60 and on the cavity 76, respectively. Thebore 82 is sized to receive therein a section of the neck portion 68 ofthe upper member 62. The transition between the bore 82 and the cavity76 defines a shoulder 86 for holding the anchor portion 70 within thecavity 76. The base member 60 preferably has a slot 80 opening on a sidethereof providing access to the cavity 76 for assembling the componentsof the plunger together.

Referring to FIGS. 11A, 11B and 11C, there is shown another embodimentof the invention where a retention pin 88 connects the upper member 62to the base member 60. In this embodiment, the anchor portion ispreferably an extension of the neck portion with a same cross-section,and is provided with a pin hole 90 extending therethrough for receivingthe retention pin 88. Similarly, the base member has a pin channel 92extending transversally therethrough, in alignment with the pin hole 90of the upper member. The pin channel 92 and pin hole 90 are sized toprovide a longitudinal clearance 78 for the pin 88 therein, therebydefining the longitudinal play between the upper member 62 and basemember 60.

FIG. 12 shows yet another embodiment of the invention, wherein the basemember 60 is provided with comprises a recess 96 extendinglongitudinally therein and opening upwardly. The resilient middleelement 64 is received at least partially within this recess 96, thebottom surface of which defining in this case the abutment surface 74.

The resilient middle element may be embodied by various resilientcomponents, which are preferably selected in view of the particularapplication to which the valve is destined. With reference to FIGS. 9Band 11A, there are shown examples of plungers where the resilient middleelement is embodied by a resilient sleeve or ring made of an appropriatepolymer or silicone material. Such an embodiment would be particularlyappropriate for applications where the required sealing force is light,as for low pressure operation. When the required sealing force is in themedium range, as for example for a few hundred pounds of processpressure into the valve, a helicoids shape spring could be use as showin FIGS. 10A and 11B. Alternatively, when the required sealing forcemust be higher, as for example for a thousand pound and higher, aBelleville type springs system could be use as show in FIGS. 10B and11C. Alternatively, the resilient middle element can consist of awasher, made for example of Teflon™, or be composed of a plurality ofcomponents combined together, such as for example a stack of discs madeof a compressible material. Advantageously, through a proper selectionof the resilient component of the resilient middle element, it istherefore possible to tune the required sealing force for a particularapplication. The plungers of a given valve may be easily disassembled tochange the middle element and therefore adapt the valve to differentpressure requirements of a given application. Alternatively, theplungers themselves may be changed or an entirely different valve may beused for different applications.

Referring to FIGS. 13, 14, 14A and 14B, there is shown anotherembodiment of the invention where a transversal play is provided betweenthe upper member and base member, thereby providing for the upper memberto be self-aligning within the corresponding passage.

With known plunger for typical diaphragm-sealed valves, slightvariations coming from the manufacturing process or the assembly processmay cause plungers to be slightly slanted or misaligned relative totheir respective plunger passage. Misalignments can also appear withtime due to extensive use and may cause a plunger to rub or scratch theinner surface of its corresponding plunger passage, leading to apremature wear of the valve. The friction of the plunger against theinner surface of the passage may generate particles which, whenaccumulating on the top surface of the plunger, eventually prevent theproper closing of the ports by the plungers. More specifically, theplungers, generally made of stainless steel, when rubbing against theinner surface of the plunger passages, also made of stainless steel,generate particles accumulating on top of the plunger, causingvariations of lengths amongst the set of plungers attached to a specificpiston, which will eventually prevent the proper closing of the ports bythe plungers and affect the overall functioning of the valve.

In some valves, plastic sleeves are placed around the plunger tofacilitate their sliding into the plunger passages. In case ofmisalignment, the base of the plunger may also rub against the sleevedsurface and generate plastic dust which may also eventually prevent theproper functioning of the valve, especially in cases where the valve hasendured extensive cycling.

In the embodiment of FIG. 13, the bore 82 and cavity 76 of the basemember 60 are sized to provide a transversal clearance 98 for the neckportion 68 and anchor portion 70 therein, thereby defining a transversalplay between the upper member 62 and base member 60. This transversalplay allows the upper member 62 of the plunger to move radially withrespect to the base member 60. As will be understood by one skilled inthe art, if the plunger 34 is misaligned or slanted relative to itscorresponding plunger passage, the upper member 62 will be able toself-align in the passage since it can move both longitudinally andtransversally with respect to the passage.

Similarly, in the embodiment of FIGS. 14, 14A and 14B, the pin channel92 and pin hole 90 are also sized to provide a transversal clearance 98for the pin 88 therein, thereby defining a transversal play between theupper member 62 and base member 60.

Both the longitudinal play and transversal play provided between thebase member 60 and upper member 62 need only be over a range sufficientto allow a slight relative movement between these components. Forexample for a typical plunger the longitudinal clearance 78 may be assmall as in the order of 0.005″ (five-thousandths of an inch) while thetransversal clearance 98 may vary between 0.002″ and 0.0020″. Of course,these measures are provided as examples only and other clearancedimensions may be used.

Of course, although the plungers shown in all the illustratedembodiments discussed above have lengths corresponding to the “longer”normally opened plungers, it will be understood that a similar structuremay equally be applied to normally closed plungers.

Referring to FIGS. 15A, 15B and 16 an alternative embodiment of theinvention is shown where the base section of each plunger is attached tothe corresponding part of the actuating mechanism of the valve throughan adjustable attachment mechanism. In this embodiment, the base member60 of the plunger has a threaded bottom portion 100, and each supportelement movable within said valve body with respect to saiddiaphragm-contacting surface, such as for example the push plate or theupper piston in the actuating mechanisms described herein, is providedwith a corresponding threaded opening 102 for receiving the threadedbottom portion of each plunger.

The plunger shown in FIG. 15A has a shorter base section as wouldtypically embody a NC plunger, whereas the plunger shown in FIG. 15B hasa length typical of a NO plunger. Both variants are shown in a valvebody in FIG. 16, where the NC plunger is affixed to the push plate andthe NO plunger is affixed to the upper piston.

In the illustrated embodiment, the push plate and the upper piston areprovided with the above-mentioned threaded openings 102 forcollaborating with a threaded bottom portion 100 of the correspondingplungers. Rotating the plunger therefore allows fine-tuning the positionof the base member of the plunger within the passage, and adjusts theeffective length of the remainder of the plunger projecting from thepush plate or upper piston. This embodiment advantageously makes itpossible to adjust the sealing force of the plungers on the diaphragmwithin the working compression range of the middle portion of theplungers. A locking set screw 104 is provided within each threadedopening 102 underneath the corresponding plunger 34 and collaboratestherewith to lock and avoid any rotation of the plunger 34 while thevalve is in use. An appropriate sealing device, such as an O-ring 106 orthe like, may be provided between the locking set screw 104 and theplunger 34 to avoid pneumatic actuation gas leaks through the piston.The use of a plunger construction where the head portion is rotationallyfree with respect to the base member, such as for example shown in FIGS.9B, 10A, 10B and 12, in combination with this embodiment would offer theadvantage of avoiding any twisting of the plunger when adjusting thebase member within the threaded opening 102.

Referring to FIG. 17, there is shown a plunger 34 according to yetanother embodiment of the invention, where the upper member 62 isgenerally “hat” shaped and is not directly interlocked with the basemember 60. In this case, the base member 60 and upper member 62 haveopposite abutment surfaces 74 and 75 facing each other, and in abutmentwith the opposite ends 72 b and 72 a of the resilient middle element 64.Preferably, the base member 60 includes a recess 96 in which theresilient middle element 64 is at least partially received the bottomsurface of the recess 96 defining the abutment surface 74 of the basemember 60.

In this embodiment, the plunger 34 is preferably used in combinationwith a spring element 108 insertable in the passage with the plunger 34to bias the upper member 62 away from the diaphragm-contacting surface.FIG. 18 shows a portion of a plunger assembly incorporating plungers 34and spring elements 108 according to this embodiment. The spring element108 may be embodied by any biaising means apt to bias the upper member62 away from the diaphragm when the plunger 34 is retracted towards theopened position.

It will be noticed that the strokes of both the upper and lower pistonsare limited by a shoulder in the valve body. As a result, an increase inactuating pressure will not move the pistons further than theirpredetermined stroke and will not change the force applied to theplungers. Preferably, the stroke of each piston is such as they willcompress the middle section of the respective plungers to the “tunevalue” without having the plunger base section forcing against the upperplunger section.

Advantageously, plungers according to embodiments of the invention maymitigate or eliminate altogether the tight requirements for plungerlengths in prior art valves. It may also allow for a greater tolerancefor variations in diaphragm thickness.

Preferably, the biasing force applied by the middle compressible sectionforce varies as a function of the ambient temperature, therebyconstituting an active temperature mechanical feedback loop built-ininto the valve mechanism. This could be for example achieved byselecting a material for the resilient middle element having anappropriate material temperature characteristic. In this manner, theforce acting against the diaphragm when the plunger is in the closedposition could be decreases as the operating temperature increases,eliminating the risk of overstressing the diaphragm.

FIG. 19 shows an example of the measured decrease in pneumatic actuatingpressure required to maintain proper sealing between ports of a typicaldiaphragm-sealed valve when the operating temperature is increased. Ascan be seen, less force is required due to the fact that the polymerbase diaphragm is softer at higher temperature. Under this operatingcondition, it is easy to deform it, and furthermore the diaphragm showbetter sealing properties at higher temperature. This is because itssurfaces is less ductile and fills more the surface finish of the valvehead.

As mentioned above, at higher temperature the diaphragm is softer, andtherefore more fragile. Maintaining the same actuating pressure than theone used at ambient temperature will have a detrimental effect on theoverall performance of the valve, which could also be permanentlydamage. Preferably temperature characteristics of the plunger'sresilient middle element are therefore selected in accordance with thetemperature characteristics of the diaphragm. As different types ofdiaphragm material and thickness can be use, different compensationmaterial characteristic could also be use.

The above example is not limitative. Those skilled in the art willunderstand that the resilient middle element of the plungers define athermal feedback loop. Base on material selection and the combinationused to make the compressible section, the system could be made todecrease, increase or maintain constant the force applied on thediaphragm when the temperatures rise.

One could also imagine that the pistons could be move by other meansthan pneumatic. Electrical mean such as solenoid or motor could also beconsidered. In the pneumatic actuation describe herein, the Bellevillesprings mounted in the bottom of the valve body are not used to set thenormally close plungers force as with prior art valve, but to set thepressure value at which the normally close ports will open, since thesealing force is fix by the compressible middle section of the plungers.This characteristic make a big difference compare to prior art. Indeed,depend on N.C. Piston Belleville washer compressibility factor, thevalve actuation pressure could be adjusted, and the time that allplungers are up (to avoid various flowpath mixing upon actuation) isalso adjustable. This is another benefit of the pneumatic base actuatorof the embodiments described above.

Of course, numerous modifications could be made to the embodimentsdescribed above without departing from the scope of the presentinvention.

The invention claimed is:
 1. A multiport gas chromatographdiaphragm-sealed valve comprising: a valve cap comprising a plurality ofprocess conduits extending therethrough, each of the process conduitsending in a process port; a valve body facing the valve cap, the valvebody comprising plunger passages extending therein and in alignment withthe respective process conduits; a diaphragm positioned between thevalve cap and the valve body, the diaphragm having temperaturecharacteristics; and a plunger assembly comprising: a plunger-actuatingmechanism located within the valve body; and a plurality ofnormally-closed and normally-opened plungers slidably fitting in therespective passages of the valve body, said plungers beingsimultaneously actuated by the plunger-actuating mechanism, each plungercomprising: a base member operatively connected to the actuatingmechanism; an upper member projecting towards the diaphragm, forpressing the diaphragm in a closed position, or extending away from thediaphragm in an opened position, the upper member having a longitudinalplay within a corresponding one of the passages with respect to the basemember; and a resilient middle element provided between the base memberand the upper member, said resilient middle element being made of amaterial which is based on the temperature characteristics of thediaphragm, the resilient middle element decreasing a sealing force onthe diaphragm when the operating temperature of the valve increases, theforce profile of the resilient element matching a varying pressureprofile required to maintain proper sealing of the plunger on thediaphragm over an operating temperature range varying from 0 to 350° C.each of said plungers thereby providing an active temperature mechanicalfeedback loop when in use within the multiport gas chromatographdiaphragm-sealed valve.
 2. The multiport gas chromatographdiaphragm-sealed valve according to claim 1, wherein for each plunger,the resilient middle element is selected from the group consisting ofrings made of a compressible material, a sleeve made of polymer orsilicone, helicoidal springs and Belleville-type springs.
 3. Themultiport gas chromatograph diaphragm-sealed valve according to claim 1,wherein the upper member of each plunger comprises a head portion forcontacting the diaphragm, and a base portion larger than the headportion, the base portion extending from and being integrally formedwith the head portion, further comprises a spring element surroundingsaid head portion to bias the upper member away from said diaphragm. 4.The multiport gas chromatograph diaphragm-sealed valve according toclaim 1, wherein the base member of each of said plungers has a threadedbottom portion, and said plunger-actuating mechanism comprises at leastone support element movable within said valve body with respect to saiddiaphragm, the at least one support element being provided with acorresponding threaded opening for receiving the threaded bottom portionof each plunger.
 5. The multiport gas chromatograph diaphragm-sealedvalve according to claim 1, wherein for each plunger: the upper membercomprises a head portion for projecting towards said diaphragm, a neckportion holding the resilient middle element and an anchor portioninterlocked and in contact with the base member, the head, neck andanchor portions being integrally part of the upper member; the basemember has an abutment surface; and the resilient middle element hasopposite ends in abutment with the head portion of the upper member andthe abutment surface of the base member, respectively.
 6. The multiportgas chromatograph diaphragm-sealed valve according to claim 5, whereinfor each plunger, the base member comprises a recess extendinginternally and longitudinally therein and opening upwardly, theresilient middle element being at least partially received within saidrecess, a bottom surface of said recess defining the abutment surface.7. The multiport gas chromatograph diaphragm-sealed valve according toclaim 5, wherein for each plunger: the anchor portion of the uppermember has a width greater than said neck portion; and the base membercomprises: a cavity for receiving said anchor portion, said cavity beingsized to provide a longitudinal clearance for the anchor portion thereinto define said longitudinal play; a bore extending longitudinallytherein and having opposite extremities opening on the abutment surfaceof said base member and said cavity, respectively, the bore being sizedto receive a section of the neck portion of the upper member therein, atransition between the bore and cavity defining a shoulder for holdingthe anchor portion within said cavity, and a transversal slot opening ona side of the base member for providing access to the cavity forremovably assembling the base member and the upper member, the bore andcavity being sized to provide a transversal clearance for the neckportion and anchor portion respectively therein, thereby defining atransversal play between the upper member and base member.
 8. Themultiport gas chromatograph diaphragm-sealed valve according to claim 5,wherein each plunger comprises a retention pin for connecting the uppermember to the base member, the base member and anchor portion of theupper member respectively have a pin channel and a pin holetransversally extending therethrough, the retention pin being insertedin said pin channel and pin hole, the retention pin having a length notexceeding a diameter of the base member, so as to allow sliding of thebase member within the corresponding passage, said pin channel and pinhole being sized to provide a longitudinal clearance for the retentionpin therein, thereby defining said longitudinal play between the uppermember and base member, said pin channel and pin hole are sized toprovide a transversal clearance for the retention pin therein, therebydefining a transversal play between the upper member and base member. 9.The multiport gas chromatograph diaphragm-sealed valve according toclaim 1 according to claim 1, wherein the at least one support elementcomprises: a push plate extending within the valve body parallel to thediaphragm and movable transversally thereto, the normally closedplungers being mounted on said push plate, a plurality of cavitiesextending across said push plate for allowing the normally open plungersto slide therethrough; and an upper piston extending under the pushplate contiguously thereto, the normally opened plungers being placedthereon.
 10. The multiport gas chromatograph diaphragm-sealed valveaccording to claim 9, wherein the plunger actuating mechanism furthercomprises: a lower piston extending under the upper piston contiguouslythereto, the lower piston being rigidly connected to the push plate;biasing means for upwardly biasing the lower piston and downwardlybiasing the upper piston; and actuating means for actuating the plungersbetween opened and closed positions thereof, the actuating mechanismcontrolling a distance between the upper and lower pistons.
 11. Themultiport gas chromatograph diaphragm-sealed valve according to claim10, wherein the valve body comprises a shoulder near the interface ofthe lower and the upper pistons, for limiting a vertical displacement ofthe lower piston.
 12. A method for adjusting a sealing force in amultiport gas chromatography diaphragm-sealed valve, the methodcomprising the steps of: a) selecting the material of the diaphragm; b)based on the material of the diaphragm selected in step a), determininga varying pressure profile required to maintain proper sealing of theplunger on the diaphragm over an operating temperature range varyingfrom 0 to 350° C. c) selecting the resilient middle element so that theforce profile of the resilient element matches the varying pressureprofile determined in step b), and d) providing the multiport gaschromatography diaphragm-sealed valve, the multiport gas chromatographydiaphragm-sealed valve comprising a valve cap with process conduitsextending therethrough, each of the process conduits ending in a processport; a valve body facing the valve cap, the valve body comprisingplunger passages extending therein and in alignment with the respectiveprocess conduits; the diaphragm selected in step a), positioned betweenthe valve cap and the valve body, and a plunger assembly comprising: aplunger-actuating mechanism located within the valve body; and aplurality of normally-closed and normally-opened plungers slidablyfitting in the respective passages of the valve body, each plungercomprising: a base member operatively connected to the actuatingmechanism; an upper member projecting towards the diaphragm, forpressing the diaphragm in a closed position, or extending away from thediaphragm in an opened position, the upper member having a longitudinalplay within a corresponding one of the passages with respect to the basemember; and the resilient middle element selected in step c), providedbetween the base member and the upper member, each of said plungersthereby providing an active temperature mechanical feedback loop when inuse within the multiport gas chromatography diaphragm-sealed valve.